1. Field of the Invention
The invention relates to walking beam furnaces and more particularly to refractory skid pads or lugs for such furnaces.
2. Prior Art
For several years, cooled walking beam furnaces have tended to replace pusher furnaces for the reheating of steel slabs, blooms or billets, by reason, in particular of their higher manufacturing capacity, their good reliability and their economic advantages.
In walking beam furnaces, the load to be heated (slabs, blooms or billets) passes from mobile beams to fixed beams successively, without friction, by controlled placing on and removing from spaced apart skid pads or lugs, integral with the walking beams and projecting over the top of the walking beams. Since the beams consist of a metallic tube (of a diameter of approx. 130-220 mm) cooled internally by a circulation of water and a relatively thick insulating refractory lining (approx. 60 mm) encasing the tube, it would be advantageous for the skid pads or lugs to be as high as possible so that their upper surface is at a temperature as close as possible to that of the inner surface of the load. Equally, the higher the skid pads or lugs, the less the effect of shadow, which the skid pads and their insulating lining may have on the heating of the load by lower lateral burners, need be feared.
However, the pads or lugs presently employed, which are made of an alloy of 50% cobalt, 30% chrome and 20% iron, have a tendency to become flattened, owing to an insufficient resistance to creep, after a few months of operation when their height exceeds a certain value (90 mm approx.), changing from an initial cylindrical shape to that of a mushroom, due to the fact that the stresses able to be supported by the metal lessen when the operational temperature of the metal increases, which is the case when the height of the skid pads or lugs is increased. For this reason, the height of present skid pads is in the range of 70-90 mm. In order to remedy this disadvantage, it has been proposed to employ an alloy rich in nickel instead of the above-mentioned alloy, but the results obtained, to the knowledge of the Applicant, have not been fully satisfactory.
Thus there is a need for skid pads or lugs of relatively large height for walking beam furnaces which perform better than the skid pads or lugs presently used and which are cheaper than these latter.